Stereophonic enhancement audio systems typically process sum (L+R) and difference (Lxe2x88x92R) signal components which, if not otherwise available, can be genrerated from a pair of left (L) and right (R) signals. The difference signal can be used to create a spatially broadened stereo image when reproduced through a pair of left and right loudspeakers or through a surround system.
Boosting the level of the difference signal with respect to the sum signal can widen such a perceived sound image. Such processing of the difference signal includes equalization comprising both bass and treble boost. However, an increase in level in the difference signal can have undesirable effects on a person""s perception of the sound. For example, boosting of the difference signal in the mid-range of audio frequencies can cause a sound perception which is undesirably very sensitive to the physical location of the listener with respect to the left and right loudspeakers. Further, the spatially broadened stereo image does not properly localize sounds which would normally emanate from the center, such as speech from a person visually centered on a display of television or motion picture programming. This is the case whether or not the sound system includes a center loudspeaker or just left and right loudspeakers.
It has been found that in a system having an increase in the level of the (Lxe2x88x92R) difference signal with respect to the (L+R) sum signal to produce a spatially broadened stereo image, that decreasing the bass response of the (L+R) sum signal along with increasing the treble response of the (L+R) sum signal helps the listener to better localize central audio material more towards the center.
For a consumer product it is necessary to keep costs low. It is herein recognized that the desired bass reduction in the (L+R) sum signal of the audio system, to help the listener to localize center audio material more towards the center, can be accomplished by the use of a gyrator to economically synthesize an inductance. A gyrator generated inductance, in combination with a resistance in the (L+R) sum signal path, economically provides such a decreasing bass frequency response while avoiding the deficiencies of a wound inductance which would be more expensive, bulky, and subject to the picking-up of hum and other electromagnetic/electrostatic extraneous noise and signals. Thus, the gyrator synthesized inductance, as well as being more economical, can be used in a lower signal level portion of the audio system.
Additionally, the equalization(s) of the (L+R) sum signal to reduce the signal at bass frequencies and to increase the signal at treble frequencies are switchable singly or in combination between xe2x80x9cONxe2x80x9d and xe2x80x9cOFFxe2x80x9d modes, and/or are adjustable singly or in combination. This switchability/adjustability permits greater flexibility to tailor the response of the system to the listener""s satisfaction.